Technical Field
The present disclosure relates to power transmission devices and power reception devices, and more particularly to a power transmission device and a power reception device used in a power transfer system in which electric power is transferred from the power transmission device to the power reception device in a contactless manner.
Description of the Background Art
Japanese Patent Laying-Open No. 2014-54095 discloses a contactless power feeding system in which electric power is supplied from a power transmission device to a vehicle in a contactless manner. In this contactless power feeding system, the power transmission device and a power reception device (vehicle) are each provided with a matching box. In the power transmission device, the input impedance of a power transmission unit is adjusted by the matching box. In the power reception device, the input impedance of a load is adjusted by the matching box (see Japanese Patent Laying-Open No. 2014-54095).
A power transmission device used in a contactless power transfer system typically includes an AC (Alternate Current) line filter provided on an AC power line connected to an AC power supply (system power supply, for example), an inverter for generating high-frequency electric power to be transmitted, a power transmission coil for transmitting electric power to a power reception coil of a power reception device in a contactless manner through an electromagnetic field, and a normal mode filter provided between the inverter and the power transmission coil. The AC line filter is connected to a ground such as a conductive enclosure. The normal mode filter is typically an LC filter. Each of the matching boxes described in Japanese Patent Laying-Open No. 2014-54095 is formed of an LC circuit, and also functions as a normal mode filter.
In such a power transmission device, a common mode current (high-frequency noise) originating from the inverter may pass between the power transmission coil and the enclosure through a parasitic capacitance formed between the power transmission coil and the conductive enclosure (ground). With the AC line filter being connected to the enclosure (ground), a loop of common mode current is formed which passes through the inverter, the power transmission coil, the parasitic capacitance, the enclosure (ground) and the AC line filter.
When the power transmission coil is included in the loop of common mode current, the high-frequency noise is emitted from the power transmission coil. In such a power transmission device, therefore, it is conceivable to provide a common mode filter between the inverter and the power transmission coil, and connect a Y capacitor (also referred to as a line bypass capacitor) of the common mode filter to the enclosure (ground).
With this circuit configuration, the emission of the high-frequency noise from the power transmission coil can be reduced. However, even with this circuit configuration, the high-frequency noise emitted from the enclosure (ground) through the AC line filter to the AC power supply may not be reduced to a sufficient degree.
Such conditions may occur in the power reception device as well. The power reception device typically includes a power reception coil for receiving electric power from the power transmission coil of the power transmission device in a contactless manner, a rectifier for rectifying the electric power received by the power reception coil, and a DC (Direct Current) filter provided on a DC power line at the output side of the rectifier. The DC filter is connected to a ground such as a conductive enclosure. Since the rectifier generates high-frequency noise, it is conceivable to provide a common mode filter between the rectifier and the power reception coil, and connect a Y capacitor of the common mode filter to the enclosure (ground), so as to suppress the emission of the high-frequency noise from the power reception coil.
With this circuit configuration, the emission of the high-frequency noise from the power reception coil can be reduced. However, even with this circuit configuration, the high-frequency noise emitted from the enclosure (ground) through the DC filter to a load connected to the DC power line may not be reduced to a sufficient degree.